Passionflower (Passiflora incarnata) has been traditionally used for its calming and sedative effects, but there is also emerging scientific evidence suggesting it may support the GABA (gamma-aminobutyric acid) system in the body. The GABA system is the primary inhibitory neurotransmitter pathway in the central nervous system, and it plays a significant role in regulating anxiety, mood, and sleep.

Several preclinical studies indicate that passionflower extracts can modulate GABAergic activity. For example, animal studies have shown that compounds found in passionflower, such as flavonoids (especially chrysin), may bind to GABA_A receptors and enhance GABA transmission, leading to anxiolytic (anxiety-reducing) and sedative effects (source). Small human clinical trials have also reported that passionflower extracts may reduce anxiety and improve sleep, possibly due to these GABAergic effects (source). However, these studies are generally limited in size and scope, and results are not always consistent.

Overall, while traditional use provides a basis for passionflower's calming effects, the current scientific evidence—though promising—is moderate and not yet definitive. Larger, well-controlled human studies are still needed to firmly establish its efficacy and mechanisms through the GABA system.